String Wound Cartridge Filters

STRING WOUND CARTRIDGE FILTER MANUFACTURER IN INDIA

High-Efficiency Depth Filtration · 0.5–150 Micron · ISO-Certified Manufacturer & Exporter

Gopani Product Systems Pvt. Ltd. is a leading string wound cartridge filter manufacturer in India, supplying precision-engineered depth filtration solutions to industrial water treatment plants, RO system builders, electroplating and surface finishing plants, chemical processors, textile dyeing units, power stations, and oil & petrochemical facilities across India and 40+ countries worldwide.

Our string wound filter cartridges deliver true depth filtration, not just surface filtration, trapping particles throughout the full depth of the wound matrix. This gives Gopani string wound filters a significantly higher dirt-holding capacity than comparable melt blown cartridges, longer service life, and lower total cost of operation.

Manufacturer Advantage: Because we manufacture in-house, we offer custom micron ratings, core materials, winding media, and OEM labelling at factory-direct prices with lead times as short as 3–5 working days for standard configurations.

What Is a String Wound Cartridge Filter?

A string wound cartridge filter (also called a wound filter cartridge, thread wound filter, depth filter cartridge, or string filter cartridge) is manufactured by precisely winding yarn, polypropylene (PP), cotton, nylon, polyester, BICO, or glass fibre, around a rigid central core in a diamond-weave pattern using CNC-controlled precision winding machines.

The unique diamond-winding pattern creates a graduated pore structure: larger pores at the outer surface progressively tighten toward the inner core. This graded density is what makes string wound filters true depth filters, particles are captured throughout the media depth, not just at the surface.

Gopani is a fully integrated ‘fibre to filter’ manufacturer. We spin our own yarn in-house before winding, giving us control over fibre denier, twist, and composition that no trading-house supplier can match. This vertical integration is why our cartridges deliver tighter pore-size tolerance across every batch.

How String Wound Filters Work, for example a 0.5 micron string wound filter:

• Contaminated fluid enters the outer surface of the wound cartridge.
• Larger particles (>20 µm) are captured in the open outer layers of the wound matrix.
• Medium particles (5–20 µm) are captured in the mid-depth layers.
• Fine particles (down to 0.5 µm) are captured in the tight inner windings near the core.
• Filtered fluid exits through the polypropylene or stainless steel core.

Because particles are held throughout the media depth, string wound cartridges hold 3-5x more dirt per unit volume than surface-type filters. This means longer filter life between changeouts, critical for high-flow industrial applications.

Gopani String Wound Cartridge Filter: Complete Specifications

Request a Sample or Get a Quote: Call / WhatsApp +91-706 901 8049 | Email: sales@gopani.com

String Wound vs Melt Blown Filter Cartridge: Comparison

One of the most common questions we hear from buyers is: ‘Should I choose a string wound or melt blown filter cartridge?’ The right answer depends on your application, fluid type, contamination profile, and budget. Here is a side-by-side comparison based on our manufacturing experience and real-world application data:

Bottom Line: For most Indian industrial water treatment, RO pre-filtration, electroplating, chemical processing, and power plant applications, string wound cartridges deliver the best cost-per-litre-filtered performance with high dirt-holding capacity. Where absolute fibre migration control is required as a final polishing step, pairing a string wound pre-filter with a melt blown final filter is the industry-standard approach.

The Clarywound Range: Gopani’s Branded String Wound Cartridge Filters

All Gopani string wound filter cartridges are manufactured under the Clarywound brand: seven purpose-engineered variants covering every application from standard industrial water treatment to high-temperature chemical processing and power plant condensate polishing. Every Clarywound cartridge is CNC precision-wound (no manual winding), contains no resin binders, lubricants, antistatic agents, or release agents, and is manufactured from FDA-grade materials.

Manufacturing philosophy: Right Yarn. Right Winding. Right Quality. Right Testing. Right Filtration. Every Clarywound cartridge starts with yarn spun in-house at Gopani’s integrated fibre facility. We do not buy yarn from the market. This ‘fibre to filter’ control is the foundation of consistent quality across batches.

Clarywound Extreme: The Art and Science of True Depth Filtration

The flagship Clarywound variant, designed where filtration performance cannot be compromised. Clarywound Extreme uses Gopani’s precision CNC winding technology to create a graded-density matrix that maximises particle capture throughout the full depth of the cartridge, not just at the surface. Available in PP, Cotton, Nylon, Polyester, BICO, and Glass Fibre yarn options; PP or SS core.

• Micron range: 0.5 to 150 µm (absolute and nominal ratings available)
• Max temp: 80°C (PP/PP core); 120°C (Cotton/SS core); 121°C (Polyester/SS core); 130°C (BICO); 140°C (Nylon/SS core); 350°C (Glass Fibre/SS core)
• Change-out DP: 0.25 MPa (2.5 bar; 36.25 psid) at 21°C
• Surface area: 0.52 ft² per 10″ standard; 0.94 ft² per 10″ jumbo
• Applications: RO pre-filtration, electroplating bath, process chemicals, water treatment, boiler feed water, effluent pre-filter
• No resin binders, lubricants, antistatic agents, or release agents

Clarywound 3X: Patented Three-Layer Depth Filtration

Clarywound 3X is Gopani’s patented multi-layer wound cartridge. Three distinct yarn densities are wound concentrically, creating defined pre-filter, intermediate, and final filtration zones within a single cartridge. This delivers significantly higher dirt-holding capacity versus single-density wound cartridges and extends service intervals in high-contamination duty cycles.

• Technology: patented three-layer gradient density winding
• Benefit: 2-3x longer service life vs. standard single-layer wound cartridges in high-solids applications
• Applications: high-turbidity borewell water; cooling tower water with heavy biological load; industrial effluent pre-filter

Clarywound Ultra: Cost-Competitive Industrial Grade

Where performance requirements are standard and cost per cartridge is the primary decision criterion, Clarywound Ultra delivers reliable depth filtration at the most competitive price point. Wound on Gopani’s CNC machines with the same quality yarn, the same manufacturing DNA as Clarywound Extreme, optimised for high-volume industrial procurement.

• Applications: municipal water pre-filtration, cooling tower pre-filter, general process water, standard RO pre-filtration
• Available in PP and Cotton yarn; PP core standard
• Ideal for: high-volume replacement buyers, OEM filter housing manufacturers, water treatment plant operators

Clarywound GF: Glass Fibre for High-Temperature and Aggressive Chemical Duty

When process temperatures exceed the limits of PP or polyester, or when the fluid chemistry would degrade organic yarns, Clarywound GF uses borosilicate glass fibre yarn on a stainless steel core. The result is a cartridge that remains structurally sound at temperatures up to 350°C and maintains chemical resistance across a wide range of acids, alkalis, and organic solvents.

• Yarn: borosilicate glass fibre; Core: SS304 or SS316
• Max temp: 350°C
• Applications: hot oil filtration, hydraulic fluid filtration, high-temperature chemical processing, hot solvent clarification, chemical plant process streams
• Chemical resistance: excellent: refer to compatibility chart or contact technical team for specific fluids

Clarywound BICO: Bicomponent Fibre for High-Temperature Depth Filtration

Clarywound BICO uses bicomponent (BICO) fibre, a specialised fibre with a polyester base construction, that achieves a higher rated temperature than standard PP while maintaining excellent chemical resistance. Rated to 130°C, BICO bridges the gap between PP (80°C) and glass fibre (350°C) for process streams in the 80-130°C range.

• Fibre type: bicomponent (BICO) with polyester base
• Max temp: 130°C
• Applications: hot process water, high-temperature chemical streams, steam condensate, elevated-temperature plating solutions

Clarywound NYLON: Nylon Yarn for Specific Chemical Compatibility

Clarywound NYLON uses nylon yarn wound around a stainless steel core, offering a distinct chemical resistance profile from PP, particularly suited to applications where PP is incompatible but glass fibre would be over-specified. Rated to 140°C with SS core.

• Yarn: Nylon; Core: SS304 or SS316
• Max temp: 140°C (Nylon/SS core)
• Applications: specific chemical streams requiring nylon compatibility; elevated-temperature filtration where PP is unsuitable

Clarywound CPU: Condensate Polishing Unit Filter for Power Plants

Clarywound CPU is engineered specifically for condensate polishing in power generation. In thermal and combined-cycle power plants, steam condensate must be recovered and polished to remove corrosion products (iron oxides, copper fines) before return to the boiler. Condensate polishing protects ion exchange resin beds and boiler tubes, directly impacting plant availability and maintenance cost.

• Application: Condensate Polishing Units (CPU) in thermal, coal, gas, and nuclear power plants
• Removes: iron oxide particulates, copper fines, suspended corrosion products from steam condensate
• Also used for: boiler condensate recovery pre-filter; steam condensate return line filtration
• Yarn: PP or Polyester per temperature; Core: SS316 standard for condensate duty
• Rating: typically 1-5 µm for fine corrosion product removal

Manufacturing method note: All Clarywound cartridges are CNC precision-wound on computer-controlled winding machines maintaining exact yarn tension and winding angle. This is the manufacturing method, not a separate product variant; it is the foundation of consistent pore-size control across the entire Clarywound range.

Applications of String Wound Cartridge Filters

String wound depth filter cartridges excel wherever fluids carry a high dissolved or suspended load and a cost-effective, high-capacity pre-filter is needed. The applications below represent core end-use markets validated by leading global manufacturers including Parker, Pall, Global Filter, ABSFil, and Serfilco, aligned with Gopani’s own installed-base experience across India and export markets.

Industry note: For electroplating and surface finishing applications, filter cartridge media cleanliness and zero extractables are critical. Gopani supplies USP-grade PP wound cartridges for plating bath use: specify ‘plating grade’ when ordering. Cotton wound cartridges should not be used in chrome or acid plating baths.

How to Select the Right String Wound Cartridge Filter

Selecting the correct string wound cartridge involves five key parameters. Getting even one wrong can result in premature filter blinding, contamination bypass, or unnecessary filter changeout costs. Here is Gopani’s selection guide:

Step 1: Determine Your Target Particle Size: What is the smallest particle size you need to remove? For RO plant pre-filtration, 5 µm or 10 µm is standard (removes silt, sand, rust). For electroplating bath filtration, 1–5 µm is typical to maintain surface finish quality. For chemical process streams, match the micron to the contaminant particle size in your fluid analysis. If in doubt, start with 5 µm and measure your pressure drop cycle.

Step 2: Know Your Flow Rate: Flow rate determines how many cartridges you need in a housing. A single 10″ cartridge handles approximately 1 m³/hr (around 17 LPM) at low pressure drop in clean water service. For 6 m³/hr (100 LPM), you need 6 × 10″ cartridges, or 3 × 20″ cartridges in a multi-round housing. For 12 m³/hr, use a 7 × 20″ housing. Contact us to size your system.

Step 3: Check Your Fluid Chemistry: If your fluid contains acids, alkalis, or solvents above 20% concentration, use PP or glass fibre. For mild applications or food contact, cotton may be used. Never use cotton with chlorinated solvents or strong oxidising agents.

Step 4: Confirm Temperature: PP cartridges (Clarywound Extreme/Ultra) are rated to 80°C. For 80–130°C, specify Clarywound BICO (polyester base, 130°C). For 130–140°C, use Clarywound NYLON (140°C with SS core). For extreme temperatures above 140°C, specify Clarywound GF glass fibre (rated to 350°C). Always use the correct grade as exceeding the rated temperature will cause cartridge deformation and bypass.

Step 5: Choose the Correct Length and Core: Standard housings accept 10″ or 20″ cartridges. Multi-round housings accept 3, 5, 7, or 10 cartridges in parallel. Specify your housing brand and size when ordering and Gopani will supply the correct fit, gasket type, and end-cap configuration.

Not sure which cartridge is right for your application? Share your water quality report, flow rate, and housing details with our technical team and we will recommend the correct filter and housing configuration, free of charge.

Get Free Filter Selection Advice: WhatsApp / Call +91-706 901 8049 or Email sales@gopani.com

Why Choose Gopani: India’s Trusted Filter Manufacturer

Certifications and Quality Compliance

Gopani’s string wound cartridge filters are manufactured under a certified Integrated Management System (IMS) covering ISO 9001:2015 (Quality), ISO 14001 (Environment), and ISO 45001 (Occupational Health and Safety). We maintain detailed batch records, raw material test certificates, and outgoing inspection records for every production run.

• ISO 9001:2015 (Quality Management System): Certified
• ISO 14001 (Environmental Management System): Certified
• ISO 45001 (Occupational Health and Safety Management System): Certified
• All three standards held together as an IMS (Integrated Management System) certification
• NSF 42 (Aesthetic Effects for drinking water treatment): Certificate available on request for potable water and drinking water system applications
• RoHS-compliant manufacturing for export to EU and UK
• FDA-grade polypropylene available for food-contact and pharmaceutical applications
• Potable water-contact materials available (WRAS-equivalent polymer grades)
• Third-party test reports available on request for export and tender orders

For government tenders, institutional procurement, or export orders requiring specific certifications or test reports, contact our quality team at quality@gopani.com. We will provide the required documentation package.

Export Supply: International Buyers

Gopani is an established exporter of string wound cartridge filters to buyers in the USA, UK, Germany, Netherlands, UAE, Saudi Arabia, Kenya, South Africa, Thailand, Vietnam, Singapore, and Australia.

For international buyers, Gopani offers:

• Factory pricing with full export documentation (commercial invoice, packing list, COO, test certificates)
• Full-container load (FCL) and less-than-container load (LCL) shipments via sea freight from JNPT / Mundra / Nhava Sheva
• Air freight for urgent small orders
• Custom labelling and packaging to buyer’s specifications
• Pre-shipment quality inspection (by buyer’s nominated agency, at buyer’s cost)
• USD / EUR / GBP invoicing available

Competitive Advantage for International Buyers: India-manufactured string wound filters from an ISO-certified direct manufacturer provide 30–50% cost savings compared to equivalent products sourced from US/European distributors, with comparable or superior quality. Lead times to port: 7–14 days for standard configurations.

International Enquiries: sales@gopani.com | WhatsApp +91-706 901 8049

Frequently Asked Questions: String Wound Cartridge Filters

Q1. What is the difference between a string wound and a spun (melt blown) filter cartridge?

A string wound filter is made by winding yarn (PP, cotton, glass fibre, nylon, polyester, or BICO) around a core in a precise CNC-controlled diamond pattern. A spun or melt blown cartridge is made by extruding thermoplastic fibres onto a core. The key difference: string wound has higher dirt-holding capacity and excels in high-contamination, high-flow duty cycles (water treatment, electroplating, chemicals), while melt blown provides a more uniform pore structure for lower fibre migration. For most industrial applications, string wound is the preferred and more economical choice. See our full comparison table above.

Q2. What micron rating should I use for different applications?

For RO plant pre-filtration, 5 µm is the standard. For high SDI feed water, use a 10 µm stage before the 5 µm stage. For electroplating bath filtration (nickel, copper, chrome), 1–5 µm is recommended to protect surface finish quality. For chemical processing streams (acids, solvents, glycol), match micron to the contaminant size, typically 5–25 µm. For power plant cooling water or DM plant pre-filters, 5–10 µm works well. For machine shop coolants, 10–25 µm is typical.

Q3. How long do string wound filter cartridges last?

Service life depends on the contamination level in the feed water, the micron rating, and the maximum allowable pressure drop. Typical service life ranges from 2 weeks (very high turbidity borewell water) to 6 months (relatively clean municipal feed water). The standard replacement trigger is when pressure drop across the housing reaches 0.5–0.7 bar above clean pressure drop.

Q4. Can string wound filters be cleaned and reused?

Generally, no. String wound cartridges are designed as single-use disposable elements. Back-flushing or cleaning typically does not restore the original pressure drop curve and can dislodge trapped particles back into the process stream. In high-cost applications, some users acid-wash or bleach-soak cotton wound cartridges, but this is not recommended by Gopani for critical applications.

Q5. What are your minimum order quantities?

For standard off-the-shelf configurations (e.g., 10″ × 1µm PP, 20″ × 5µm PP), there is no minimum order; we supply from single cartridges for replacement needs up to full container loads for industrial buyers. For custom specifications (non-standard length, special core, OEM labelling), the minimum order is typically 500–1000 pieces depending on the configuration. Contact our sales team for a specific quote.

Q6. Do your cartridges fit all standard filter housings?

Yes. Gopani string wound cartridges are manufactured to ANSI/NSF standard outer diameter and length dimensions and fit all standard DOE (double open end) and SOE (single open end) housings from any manufacturer, including Pentek, Harmsco, 3M, Parker, Filtraflo, and Indian-made housings. Please specify your housing model when ordering to ensure the correct end-cap configuration.

Q7. Do you supply filter housings as well?

Yes. Gopani manufactures a complete range of filter housings in PP, stainless steel (SS304/SS316), and FRP: single-round, multi-round, and jumbo big-blue configurations. Buying cartridges and housings together from a single manufacturer ensures dimensional compatibility, reduces procurement complexity, and gives you a single point of accountability.

Q8. How do I order samples before committing to a bulk order?

We offer sample packs (typically 5–10 cartridges) for qualified buyers conducting product evaluation. Please contact sales@gopani.com with your application details, required micron, length, and current supplier information. We will arrange a sample shipment within 2–3 working days.

Q9. Which Clarywound variant should I choose for my application?

The right Clarywound variant depends on your fluid temperature, chemistry, and performance requirement. Clarywound Ultra covers standard industrial water and general process water up to 80°C. Clarywound Extreme is the choice when consistent quality and tighter pore control matter. Clarywound BICO handles temperatures up to 130°C with polyester base chemistry. Clarywound NYLON is selected where nylon compatibility is needed up to 140°C. Clarywound GF (glass fibre) covers extreme temperatures to 350°C and aggressive chemical duty. Clarywound 3X delivers extended service life in high-contamination applications. Clarywound CPU is the dedicated power plant condensate polishing grade. Share your fluid details, temperature, and flow requirements and our technical team will confirm the right variant.

Q10. What is Clarywound BICO and what makes bicomponent filtration different?

BICO stands for bicomponent fibre, a specialised yarn with a polyester base construction that achieves higher thermal stability than standard PP yarn. Clarywound BICO is rated to 130°C, bridging the gap between PP (80°C limit) and glass fibre (350°C) for process streams in the 80-130°C range. The polyester base gives excellent chemical resistance and structural integrity at elevated temperatures. BICO is commonly specified for hot process water, elevated-temperature plating solutions, and steam condensate applications.

Q11. Does Gopani make its own yarn, or do you buy from the market?

Gopani is a fully integrated ‘fibre to filter’ manufacturer. We spin our own PP yarn in-house at our Ahmedabad facility before the winding process begins. This is a significant distinction from trading houses or assembly-only manufacturers who source yarn externally. In-house yarn production means we control the fibre denier, tensile strength, and chemical purity from raw material to finished cartridge. This is how we maintain consistent filtration performance across production batches and why Gopani cartridges meet OEM quality standards for export markets in Europe, North America, and the Middle East.

Q12. When should I specify non-foaming PP grade for Clarywound cartridges?

Non-foaming PP grade is specified when the filter cartridge is used in chemical dosing systems, surfactant-containing process streams, or any application where standard PP compounds can contribute to foaming in the downstream process. Standard PP compounds contain minor processing additives that, in some surfactant-rich fluids, can act as nucleation sites for foam. Non-foaming PP grade uses a specially compounded resin with these additives removed. It is available across the Clarywound range on request: specify ‘non-foaming PP grade’ when ordering or on your purchase order.

Request a Quote or Sample

Talk to our technical team for a free filter selection consultation. We supply from single-cartridge replacement orders to full industrial contract volumes, with lead times as short as 3–5 working days for standard grades.

ISO 9001:2015 Certified Manufacturer · 40+ Years Manufacturing Experience · Direct Factory Pricing · Exports to 40+ Countries